fix(react19): remove React 19 incompatible APIs and restore compatibility

[kkarthik-eightfold]

SUMMARY:

Makes @eightfold.ai/octuple compatible with React 19 so it can be consumed by Talent Forge, by removing all removed/incompatible React 19 APIs while preserving public APIs and existing behavior.

React 19 removed ReactDOM.render, ReactDOM.unmountComponentAtNode, and ReactDOM.findDOMNode, and moved element refs from a top-level .ref property onto props.ref. These broke Octuple in several places:

• DialogHelper used ReactDOM.render/unmountComponentAtNode directly, which made the whole @eightfold.ai/octuple barrel import fail under React 19. Migrated to createRoot/root.render/root.unmount from react-dom/client, tracking one root per container id so close() unmounts the right instance. Public show()/showSmall()/showMedium()/close() APIs are unchanged.

• findDOMNode.ts, SingleObserver.tsx, CSSMotion.tsx, Trigger.tsx, useHeights.tsx all depended on ReactDOM.findDOMNode (directly or via the shared findDOMNode() helper) to resolve a DOM node from a component that couldn't accept a ref. findDOMNode() is now a null-safe passthrough with no ReactDOM dependency. DomWrapper (the SingleObserver/CSSMotion fallback) now resolves the DOM node via a hidden marker node instead, placed after (not before) its children so container.firstChild/:first-child semantics are preserved; the marker is only rendered at all when a direct ref genuinely can't be attached (see canAttachRef in ref.ts), so Table's <td> (which must stay a direct child of <tr>) and other host/forwardRef children get zero extra DOM nodes.

• Added canAttachRef() and getElementRef() to ref.ts. getElementRef() reads props.ref on React 19 and falls back to the legacy top-level .ref on React 16.8–18 (Octuple's peerDependencies still span that range) — reading props.ref alone silently drops real refs on React <19, which broke Align's forceAlign wiring inside PopupInner until this was corrected. Rolled out across SingleObserver, CSSMotion, Trigger, Align, and useItemRef.

• react-is@18 doesn't recognize React 19 elements (different $$typeof symbol), and react-is@19 doesn't recognize React <19 elements — react-is versions are generation-locked, not version-range compatible. Since a single bundled react-is version can't correctly serve every React major Octuple supports, toArray.ts's Fragment detection and ref.ts's forwardRef detection now check the relevant symbols directly instead of delegating to react-is. Bumped react-is/@types/react-is to 19.x per the target anyway.

• @react-spring/web's peerDependencies already allow React 19; left unchanged.

• Added a global.d.ts ambient declaration for react-dom/client so the build type-checks against this repo's own React 17 devDependency, which predates that module.

GITHUB ISSUE (Open Source Contributors)

N/A

JIRA TASK (Eightfold Employees Only):

N/A

CHANGE TYPE:

• Bugfix Pull Request
• Feature Pull Request

TEST COVERAGE:

• Tests for this change already exist
• I have added unittests for this change

Added: DialogHelper.test.tsx (mount/unmount via createRoot), findDOMNode.test.ts (null-safety), reactIs.test.tsx (React 19 Fragment detection via toArray), plus rewritten cases in CSSMotion.test.tsx (DOM resolution without findDOMNode). Updated 35 pre-existing snapshots (Select, SkillBlock, DatePicker) that gained the new hidden DomWrapper marker node, after confirming each is the accepted, documented trade-off.

TEST PLAN:

• yarn typecheck — pass
• yarn lint — pass
• yarn test — 225/225 suites, 2657/2679 tests pass (22 pre-existing skips), 441/441 snapshots pass
• yarn build (rollup) — succeeds, including the react-dom/client import
• Manually verified no remaining ReactDOM.render/unmountComponentAtNode/ReactDOM.findDOMNode/legacy element.ref usage in src

Known limitations / follow-ups

• This repo's own devDependencies remain on React 17 (bumping them breaks the 144-file Enzyme-based test suite, which has no official React 18/19 adapter), so DialogHelper.test.tsx uses a virtual jest.mock('react-dom/client', ...) shim backed by React 17's ReactDOM.render/unmountComponentAtNode to exercise the public API against this repo's own toolchain. Real consumers on React 18/19 get the real module. A follow-up to migrate the test suite off Enzyme would let this repo verify against a real React 19 install directly.
• Found and flagged separately (not fixed here, out of scope): Dialog.tsx accepts a parent prop but never forwards it to BaseDialog, so DialogHelper always portals into document.body regardless of the container it creates. Pre-existing, unrelated to React 19.
• 6 components (Tree, DirectoryTree, BaseTree, Table, OcTable, plus TreeNode's class component) set .defaultProps on function/forwardRef components. React 19 still supports this but logs a deprecation warning; not addressed here since it doesn't break functionality and wasn't part of the original investigation's scope.

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[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.21%. Comparing base (fac8548) to head (491ca41).

Files with missing lines	Patch %	Lines
src/components/Dialog/DialogHelper.tsx	88.00%	3 Missing ⚠️
src/shared/utilities/ref.ts	86.66%	2 Missing ⚠️
...d/ResizeObserver/SingleObserver/SingleObserver.tsx	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1158      +/-   ##
==========================================
+ Coverage   85.07%   85.21%   +0.13%     
==========================================
  Files        1230     1230              
  Lines       21593    21653      +60     
  Branches     8211     8243      +32     
==========================================
+ Hits        18370    18451      +81     
+ Misses       3137     3118      -19     
+ Partials       86       84       -2     

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